Details
Configuring any SSL settings for xpack.security.transport.ssl without also configuring xpack.security.transport.ssl.enabled generates warnings in the deprecation log. In 8.0, this configuration will result in errors.

Impact
To avoid deprecation warnings, either:

If you want to enable SSL, follow the instructions to encrypt internode communications with TLS. As part of this configuration, explicitly set xpack.security.transport.ssl.enabled as true.

For example:

xpack.security.transport.ssl.enabled: true 
xpack.security.transport.ssl.keystore.path: elastic-certificates.p12
xpack.security.transport.ssl.truststore.path: elastic-certificates.p12

Details
Configuring any SSL settings for xpack.security.http.ssl without also configuring xpack.security.http.ssl.enabled generates warnings in the deprecation log. In 8.0, this configuration will result in errors.

Impact
To avoid deprecation warnings, either:

If you want to enable SSL, follow the instructions to encrypt HTTP client communications for Elasticsearch. As part of this configuration, explicitly set xpack.security.http.ssl.enabled as true.

For example:

xpack.security.http.ssl.enabled: true 
xpack.security.http.ssl.certificate: elasticsearch.crt
xpack.security.http.ssl.key: elasticsearch.key
xpack.security.http.ssl.certificate_authorities: [ "corporate-ca.crt" ]

Details
Enabling SSL for the transport interface without also configuring a certificate and key through use of the xpack.security.transport.ssl.keystore.path setting or the xpack.security.transport.ssl.certificate and xpack.security.transport.ssl.key settings generates warnings in the deprecation log. In 8.0, this configuration will result in errors.

Impact
If xpack.security.transport.ssl.enabled is set to true, provide a certificate and key using the xpack.security.transport.ssl.keystore.path setting or the xpack.security.transport.ssl.certificate and xpack.security.transport.ssl.key settings. If a certificate and key is not provided, Elasticsearch will generate warnings in the deprecation log.

Details
Enabling SSL for the HTTP layer without also configuring a certificate and key through use of the xpack.security.http.ssl.keystore.path setting or the xpack.security.http.ssl.certificate and xpack.security.http.ssl.key settings generates warnings in the deprecation log. In 8.0, this configuration will result in errors. Impact
If xpack.security.http.ssl.enabled is set to true, provide a certificate and key using the xpack.security.http.ssl.keystore.path setting or the xpack.security.http.ssl.certificate and xpack.security.http.ssl.key settings. If a certificate and key is not provided, Elasticsearch will generate warnings in the deprecation log.

Details
In 8.x, Elasticsearch will only read indices created in version 7.0 or above. An 8.x node will not start in the presence of indices created in 6.x or earlier versions of Elasticsearch.

Impact
Before upgrading to an 8.x version, reindex any index created in 6.x or earlier versions with Elasticsearch 7.x. If you no longer need the index, delete it instead. You can use the get index API to check the Elasticsearch version in which an index was created.

GET *,-.*?human=true&filter_path=**.settings.index.version.created_string

Details
The simplefs value for the index.store.type index setting is now deprecated. Use the niofs value for superior or equivalent performance instead.

Impact
To avoid deprecation warnings, discontinue use of the simpleifs store type in new indices or index templates. Reindex any index using simplefs into one with another store type.

Details
In 6.0, we deprecated the accept_default_password cluster setting. We removed support for default passwords in 6.0 but did not remove the setting for backwards compatibility. In 8.0, we will remove the setting.

Impact
To avoid deprecation warnings, discontinue use of the setting.

Details
In 5.2, we deprecated the following cluster settings:

These native role cache settings have been unused since 5.2, but we did not remove the settings for backwards compatibility. In 8.0, we will remove the settings.

Impact
To avoid deprecation warnings, discontinue use of the settings.

Details
In 6.2, we deprecated support for fractional byte size values, such as 23.5pb, in:

Impact
To avoid deprecation warnings, discontinue use of fractional byte size values in your configurations. Update any existing configurations to use whole values.